Abaixo está uma instrução que descreve uma tarefa de geração de SQL, combinada com uma entrada que fornece mais contexto sobre os esquemas de tabela disponíveis. Escreva o código SQL que responda adequadamente à solicitação
 ###Instrução: Qual taxa de compressão tem um nome DX 10 (nenhum) e um FOURCC de dxt4?
 ###Tabelas: CREATE TABLE s3tc_format_comparison (s3tc_format_comparison_id AUTO_INCREMENT PRIMARY KEY, FOURCC VARCHAR, DX 10 Name VARCHAR, Description VARCHAR, Alpha premultiplied? VARCHAR, Compression ratio VARCHAR, Texture Type VARCHAR) CREATE TABLE series_5 (series_5_id AUTO_INCREMENT PRIMARY KEY, Episode VARCHAR, First aired VARCHAR, Entrepreneur(s) VARCHAR, Company or product name VARCHAR, Money requested (£) INT, Investing Dragon(s) VARCHAR) CREATE TABLE percussion_scholastic_open_class (percussion_scholastic_open_class_id AUTO_INCREMENT PRIMARY KEY, Ensemble VARCHAR, Gold Medals INT, Silver Medals INT, Bronze Medals INT, Total Medals INT) CREATE TABLE virginia_counties_and_cities_ranked_by_per_capita_income (virginia_counties_and_cities_ranked_by_per_capita_income_id AUTO_INCREMENT PRIMARY KEY, County or City VARCHAR, Per capita income VARCHAR, Median household income VARCHAR, Median family income VARCHAR, Population INT, Number of households INT) CREATE TABLE season_effects (season_effects_id AUTO_INCREMENT PRIMARY KEY, Storm name VARCHAR, Dates active VARCHAR, Max 1-min wind mph (km/h) VARCHAR, Min. press. ( mbar ) VARCHAR, Damage (millions USD ) VARCHAR, Deaths VARCHAR)  
SELECT Compression ratio FROM s3tc_format_comparison WHERE DX 10 Name = (none) AND FOURCC = dxt4